1. Field of the Invention
The invention relates to fiber reinforced foamed plastic products employing unsaturated polyester resins in matched dies.
2. Description of the Prior Art
Fiber reinforced plastic articles employing unsaturated polyester resin compositions have been fabricated in matched dies for many years. Some of the products which have been fabricated in this fashion include automotive parts such as fenders, corner moldings, ducting, electrical parts such as switch gear housings, and the like. The products have been fabricated in relatively expensive matched metal dies maintained under substantial pressures during the cure. Low pressure matched die molding also is known. The cavity molding of foamable resins such as polyurethane foam resins in combination with reinforcing fibers also is known.
Foamable unsaturated polyester resin compositions containing azo blowing agents are known. See U.S. Pat. application Ser. No. 516,821, 21, filed Oct. 21. 1974, and now U.S. Pat. No. 3,954,274 assigned to the assignee of this invention. The use of such foamable unsaturated polyester resin compositions containing azo blowing agents in spray-up fiber reinforced plastic products is known. See U.S. Pat. application Ser. No. 584,608, filed June 6, 1975 and now abandoned, assigned to the assignee of this invention.
When unsaturated polyester resins are employed in matched die molding processes, there are two customary procedures available. In the first procedures, the polyester resin and glass fibers are combined into a product known as a bulk molding compound or a sheet molding compound which also contains a high temperature polymerization initiator for the curing of the resin ingredient. The mixture of fibers and resin along with other particulate inert fillers if desired is placed in a mold cavity between matched dies; the dies are brought together in compression and are heated to activate the high temperature polymerization initiator. The other procedure, known as a wet molding process, involves lining a mold cavity with fibrous reinforcement, sometimes randomly and sometimes precut and/or preshaped as a molding preform. Liquid unsaturated polyester resin along with a high temperature initiator is poured on top of the reinforcing fibers and the mold is closed so that the wet polyester resin fills the mold cavity and wets the reinforcing fibers. The mold cavity is retained in its closed position until the polyester resin has cured.